The present invention relates to a laminate film which is outstanding in its oxygen and water vapour barrier properties, and to a vapour-deposited film employing same.
For the purposes of storing foods and pharmaceutical products over a long period of time, it is necessary to carry out packaging which is outstanding in its gas barrier properties, that is to say which has the effect of preventing penetration from outside of the oxygen and water vapour which accelerate deterioration and putrefaction. In recent years, there has been an increasing demand that the film packaging with outstanding gas barrier properties used for this purpose be transparent in order to enable, in particular, the state of the contents to be ascertained.
Now, as an example of non-transparent packaging which possesses high-level gas barrier properties, there is known film packaging where aluminium foil has been laminated but, when compared to polymer film, aluminium foil has poor flexing characteristics and pinholes are produced by, for example, folding-over during processing and the like, so the gas barrier properties are easily impaired, and hence there is desired a replacement film having high-level gas barrier properties matching aluminium foil.
As examples of transparent gas barrier films, there are known those where polyvinylidene chloride or ethylene/vinyl alcohol copolymer is laminated. Moreover, it is already well-known that where metal compounds are formed on a polymer film the gas barrier properties and transparency are good.
However, conventional transparent gas barrier films have problems of the following kind. Polyvinylidene chloride resin or ethylene/vinyl alcohol copolymer resin laminate films are inadequate in their oxygen and water vapour gas barrier properties and, in particular, there is a marked lowering thereof in high temperature sterilization treatments. Furthermore, when incinerated, polyvinylidene chloride produces chlorine gas and there are concerns about its effects on the terrestrial environment.
On the other hand, film where a coating of silicon oxide or aluminium oxide has been formed by vapour-deposition has excellent barrier properties but, in recent years, as eating habits have become more sophisticated, and along with the appearance of various different kinds of food products and cakes/confectionary on the market, the enhancement of properties such as the barrier properties and the prolonged maintenance of product quality have come to be regarded as even more important. In particular, in the packaging of snack confectionary and foods, gas barrier properties which exceed those achieved hitherto have begun to be demanded to prevent oxidation or dampening of the contents, and in order to ensure fresh quality over a long period.
In order to meet such requirements, for example in JP-A-10-29264 there is described the provision of an inorganic vapour-deposited layer on a polyamide film; in JP-A-7-223305 there is described a polyester/aromatic polyamide laminate film; and in JP-A-9-174777 there is described the provision an inorganic vapour-deposited layer on the polyester side of a polyamide/modified-polyester laminate film. While the gas barrier properties are certainly improved thereby, they do not achieve the high levels recently demanded.
Consequently, the objective of the present invention lies in overcoming the problems of the prior art and, with the aim of markedly enhancing the gas barrier properties in respect of oxygen and water vapour of vapour-deposition film, offering a film for vapour deposition which is made to manifest outstanding gas barrier properties; together with a vapour-deposited film employing same.
The present invention relates to a laminate film where a polyester film or an aliphatic polyamide film is employed as a substrate layer (the A layer), and where a polyamide layer (the C layer) in which the chief component is an aromatic polyamide of glass transition temperature at least 60xc2x0 C. is employed as a layer to undergo vapour deposition, and the centre-line average roughness (Ra) of the face which is to undergo vapour deposition is in the range 0.005 to 0.03 xcexcm. Furthermore, the present invention relates to a laminate film where a polyester film or an aliphatic polyamide film is employed as a substrate layer (the A layer), and where a polyamide layer (the C layer) in which the chief component is an aromatic polyamide of glass transition temperature at least 60xc2x0 C. is employed as a layer to undergo vapour deposition, and between the A layer and the C layer there is interposed a layer (the B layer) comprising polymer of SP value 10 to 15. Moreover, the present invention also relates to a packaging film where an inorganic thin film has been vapour-deposited on the vapour-deposition face of said laminate film.
Optimum Form for Practising the Invention
Polyester film in the present invention refers to a polymer film comprising a dicarboxylic acid component and a glycol component. Examples of the dicarboxylic acid component are isophthalic acid, terephthalic acid, phenyl-4,4xe2x80x2-dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalene-2,7-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, diphenoxyethane-4, 4xe2x80x2-dicarboxylic acid, diphenylsulphone-4,4xe2x80x2-dicarboxylic acid, diphenylether-4,4xe2x80x2-dicarboxylic acid, malonic acid, 1,1-dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, decamethylenedicarboxylic acid and the like but, amongst these dicarboxylic acid components, film comprising an acid component in which the chief component is terephthalic acid and/or 2,6-naphthalenedicarboxylic acid, is preferred. If the chief component is other than terephthalic acid or 2,6-naphthalenedicarboxylic acid, the adhesive strength of the vapour-deposited film tends to be inferior and it may be difficult to obtain outstanding gas barrier properties.
On the other hand, examples of the glycol component are glycol components such as ethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, 1,3-propanediol and other such aliphatic glycols, cyclohexanedimethanol and other such alicyclic glycols, and bisphenol A, bisphenol S and other such aromatic glycols, and also polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymer materials such as polyethylene glycol/propylene glycol copolymer but, of these, a glycol component in which ethylene glycol is the chief component is preferred. With other than ethylene glycol as the chief component, the adhesive strength of the vapour-deposited film tends to be inferior and it may be difficult to obtain outstanding gas barrier properties. Now, there may be jointly used two or more such dicarboxylic acid components and/or glycol components.
Other polyesters can be incorporated into the polyester film within a range such that the effects of the invention are not impaired. Examples of such other polyesters are polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), polyhexamethylene terephthalate (PHT), polyethylene naphthalate (PEN), polycyclohexane-dimethylene terephthalate (PCT), polyhydroxybenzoate (PHB) and copolymer resins thereof.
Furthermore, aliphatic polyamide film in the present invention refers to a polyamide film obtained by the ring opening polymerization of a lactam, the polycondensation of an aminocarboxylic acid or the polycondensation of a diamine and dicarboxylic acid. Specific examples are polyamide 6, polyamide 12, polyamide 11, polyamide 6-6, polyamide 6-10, polyamide 6-12 and copolymers or mixtures thereof.
The film of the present invention needs to have a substrate layer selected from polyester films and aliphatic polyamide films and, in terms of the vapour-deposition processability, a polyester film is preferred.
The aromatic polyamide in the present invention is a polyamide in which at least 85 mol % of the amide bonds are obtained from a aromatic diamine and/or an aromatic dicarboxylic acid component. Specific examples thereof are poly-p-phenylene terephthalamide, poly-m-phenylene terephthalamide, poly-p-benzamide, poly-4,4xe2x80x2-diaminobenzamide, poly-p-phenylene-2,6-naphthalicamide, copoly-p-phenylene/4,4xe2x80x2-(3,3xe2x80x2-dimethylbiphenylene)-terephthalamide, copoly-p-phenylene/2,5-pyridylene-terephthalamide, poly-o-phenylene naphthalamide, poly-m-phenylene phthalamide, poly-p-phenylene phthalamide, poly-o-phenylene isophthalamide, poly-m-phenylene isophthalamide, poly-p-phenylene isophthalamide, poly-o-phenylene terephthalamide, poly-1,5xe2x80x2-naphthalene phthalamide, poly-4,4xe2x80x2-diphenylene-o-phthalamide, poly-1,4-naphthalene phthalamide, poly-1,4-naphthalene isophthalamide, poly-1,5-naphthalene isophthalamide, and aromatic amides containing alicyclic amines typified by those where some of the benzene rings of the aromatic diamines in the aforesaid polymers are replaced by piperazine, 1,5-dimethylpiperazine or 2,5-diethylpiperazine, or aromatic polyamide copolymers containing two phenylene groups which are linked by means of an ether linkage, for example when the aromatic diamine is 3,3xe2x80x2-oxydiphenylenediamine or 3,4xe2x80x2-oxydiphenylenediamine, or by xe2x80x94Sxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NHxe2x80x94 or the like, examples of which are poly-3,3xe2x80x2-oxyphenyleneterephthalamide/poly-p-phenylene terephthalamide copolymer, poly-3,4xe2x80x2-oxydiphenylene terephthalamide/poly-p-phenylene terephthalamide copolymer and the like.
It is necessary that there be laminated to at least one face of the substrate layer selected from polyester film and aliphatic polyamide film, a polyamide C in which the chief component is, from amongst the aforesaid aromatic polyamides, an aromatic polyamide of glass transition temperature at least 60xc2x0 C. If the glass transition temperature is less than 60xc2x0 C., it is difficult to obtain outstanding barrier properties of the vapour-deposited film, so this is undesirable. More preferably, the glass transition temperature is at least 80xc2x0 C. and still more preferably at least 100xc2x0 C. The upper limit of glass transition temperature in the case of aromatic polyamides is about 120xc2x0 C., and so the substantial upper limit of glass transition temperature is 120xc2x0 C.
The laminated thickness of the C layer is preferably in the range 0.01 to 5 xcexcm. With less than 0.01 xcexcm, it is difficult to obtain outstanding vapour-deposited barrier properties, so this is undesirable. Conversely, if the laminated thickness exceeds 5 xcexcm then, depending on the thickness of the substrate layer, curling of the film tends to occur and handling is impaired, so this is undesirable. More preferably, the laminated thickness is 0.05 to 5 xcexcm and still more preferably it is 0.1 to 5 xcexcm.
In the film of the present invention, it is preferred that a B layer comprising a single polymer, or a plurality of polymers, of SP value (solubility parameter) 10 to 15 be interposed between the substrate layer, that is to say the A layer comprising polyester film or aliphatic polyamide film, and the polyamide C layer. In the case where the A layer is an aliphatic polyamide film, then there need not necessarily be interposed a polymer B layer, but in the case where the A layer is a polyester film, if no polymer B layer is interposed, problems such as layer separation tend to arise, so it is preferred that a B layer be interposed.
Here, SP values (solubility parameters) are numbers which denote the compatibility of compounds, and the SP value can be determined by a measurement means such as the latent heat of evaporation method, the vapour pressure method, the dissolution method, the swelling method, the surface tension method, the critical pressure method or the thermal expansion coefficient method, or by calculation based on the molecular attraction constant method using the molecular attraction constants proposed by Small, Hoy et al (Hoy K L, J. Paint Technol. 42(541)76-(1970), Small Pa., J. Appl. Chem. 3, 71-(1953)).
In the film of the present invention, the polymer B layer is preferably composed of a polyester D and a polyamide E. As polyester D, there may be used a polyester of the same kind as described above, or there can be used another polyester. As polyamide E, there may be used an aforesaid aliphatic polyamide or aromatic polyamide, or a mixture of the two, but, in terms of the adhesion properties, it is preferred than an aromatic polyamide be used. In terms of the adhesion properties, the compositional ratio (weight ratio) of polyester D/polyamide E in the polymer B layer is preferably from 90/10 to 10/90.
The laminated thickness of the polymer B layer is not particularly restricted but, from the point of view of the adhesion properties, 0.1 to 10 xcexcm is preferred and 0.2 to 5 xcexcm is more preferred.
The lamination method is not particularly restricted and examples include the method of lamination by coating and the method of lamination by co-extrusion, with the method based on co-extrusion being particularly preferred in terms of the adhesion properties of the respective layers, and the oxygen and water vapour barrier properties.
In the case of the film of the present invention, it is preferred that the centre-line average roughness (Ra) of at least one face of the polyamide C layer be 0.005 to 0.03 xcexcm. More preferably, it is 0.008 to 0.025 xcexcm, and still more preferably 0.01 to 0.02. If Ra is less than 0.005 xcexcm, the film handling characteristics tend to be impaired, so this is undesirable. If Ra exceeds 0.03 xcexcm, then as well as the resistance to scratching being impaired, pin holes are readily produced at the time of the vapour-deposition, so this is undesirable. There are no restrictions on the method for ensuring Ra lies within the aforesaid range, but the method of incorporating particles into the substrate layer is preferred, and there may also be used the method of using a metal drum with a textured surface to transfer the texture at the drum surface to the film.
The film of the present invention preferably has a substrate layer planar orientation coefficient (fn) lying in the range 0.155 to 0.180, and more preferably in the range 0.1625 to 0.175. If fn is less than 0.155 then, since the film orientation is lowered, there is a lowering of strength and the film is readily stretched by external forces, and the processing suitability tends to be reduced, so this is undesirable. Conversely, if it exceeds 0.180, film widthwise-direction variation in properties and whitening readily occur, so this is undesirable.
The film of the present invention will preferably have a percentage heat shrinkage, measured at 150xc2x0 C. for 30 minutes, of 0.5 to 2% in the film lengthwise direction and xe2x88x921.2 to 0.5% in the widthwise direction, and more preferably 1 to 2% in the film lengthwise direction and xe2x88x921 to 0% in the widthwise direction. In the case where the heat shrinkage exceeds 2% in the film lengthwise direction or exceeds 0.5% in the widthwise direction, or again if the film extends more than 1.2% in the widthwise direction, dimensional changes readily occur at the time of vapour-deposition, or during processing when an external force is applied such as during lamination or printing, so this is undesirable. It is preferred that the lengthwise direction heat shrinkage at 150xc2x0 C. for 30 minutes be as small as possible but, since there is an inevitable 0.5% lengthwise shrinkage, the lower limit of heat shrinkage in the lengthwise direction is essentially 0.5%. Now, a minus (xe2x88x92) value of heat shrinkage here denotes elongation.
In the present invention, the difference in Ra between that of the face which is to undergo vapour-deposition and that of the face which is not to undergo vapour-deposition (xcex94Ra) is preferably in the range 0.003 to 0.045 xcexcm. It is further preferred that xcex94Ra be 0.005 to 0.045 xcexcm. Ra for the face which is not subjected to vapour-deposition is preferably 0.008 to 0.05 xcexcm, and more preferably 0.01 to 0.03 xcexcm. If Ra for the face not subjected to vapour deposition exceeds 0.05 xcexcm, the slipperiness is too great, and instead the vapour-deposition characteristics and processability are impaired, for example the handling properties are adversely affected, so this is undesirable.
The particles added to the film of the present invention are not particularly restricted providing they are inactive in terms of the polyester but, as examples of the added particles, there are inorganic particles, organic particles, crosslinked polymer particles and particles which are internally-produced within the polymerization system. Two or more types of such particles may be added. The amount added is preferably from 0.01 to 10 wt % and more preferably from 0.02 to 1 wt %. The average size of the particles added is preferably 0.001 to 10 xcexcm and more preferably 0.01 to 2 xcexcm. If the average particle size exceeds 10 xcexcm, film defects tend to be produced, which is undesirable.
The inorganic particles used are not particularly restricted and examples include calcium carbonate, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulphate, barium sulphate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminium oxide, silicon oxide, titanium oxide, zirconium oxide, lithium fluoride and the like.
Examples of the organic particles are calcium oxalate, and the terephthalic acid salts of calcium, barium, zinc, manganese, magnesium and the like.
Examples of the crosslinked polymer particles are the homopolymers or copolymers of vinyl monomers such as divinyl benzene, styrene, acrylic acid and methacrylic acid. Furthermore, organic fine polymer particles of polytetrafluoroethylene, benzoguanamine resins, thermosetting epoxy resins, unsaturated polyester resins, thermosetting urea resins, thermosetting phenolic resins and the like are also favourably employed.
As particles internally-produced within the polymerization system, there can be used those produced by the known method of adding an alkali metal compound or alkaline earth metal compound to the reaction system, and also by further adding a phosphorous compound.
Optionally, in the film of the present invention, there can be incorporated flame retardants, heat stabilizers, antioxidants, UV absorbers, antistatic agents, pigments, dyes, fatty acid esters, waxes or other organic lubricants, or antifoaming agents such as a polysiloxane.
The thickness of the film of the present invention is not particularly restricted but it is preferably 1 to 3.00 xcexcm and more preferably 5 to 100 xcexcm.
The film structure may be a two-layer laminate of A/C, a three-layer laminate of A/B/C or a multi-layer laminate with more than three layers, and the lamination thickness ratio may be freely set. Furthermore, there may also be laminated layers other than these, for example an antistatic layer, a matt layer, a hard coat layer, a ready-slip coating layer, a ready-adhesion layer, a tacky adhesion layer or the like.
In the case of the film for vapour-deposition of the present invention, by subjecting the surface of the polyamide C layer which is to undergo vapour-deposition to a corona discharge treatment and raising the surface wetting tension to at least 35 mN/m, the adhesion of the vapour-deposited inorganic thin film is enhanced, so this is preferably employed. The gas atmosphere at the time of the corona discharge treatment may be air, carbon dioxide or a mixed nitrogen/carbon dioxide system, and when, in particular, the corona treatment is carried out in carbon dioxide gas or in a mixed nitrogen/carbon dioxide gas (volume ratio in the range from 95/5 to 50/50) ,the surface wetting tension of the film is raised to 35 mN/m or above, so this is preferred.
As the inorganic thin film there can be favourably used an aluminium thin film and/or an oxide of a metal such as aluminium, silicon, zinc, magnesium or the like. Amongst the metal oxides, the use of an aluminium oxide thin film is further preferred from the point of view of gas barrier properties and cost. The metal oxide may be just one of the aforesaid oxides or it may be a mixture thereof, and some metal component may also remain.
Ordinary vacuum deposition can be employed as the method for forming these inorganic thin films by vapour-deposition but there can also be used methods such as ion plating or sputtering, or activation of an evaporated material with a plasma. With regard to the method of forming a metal oxide, there may be favourably employed, from the point of view of productivity, the method of building-up the metal oxide by direct evaporation of a metal oxide, or by reactive vapour-deposition in an oxidizing atmosphere. Again, chemical gas phase vapour deposition methods (so-called CVD methods) can be used as vapour deposition methods in the broad sense. An oxidizing atmosphere refers to the introduction into the vacuum deposition device, in the required amount, of oxygen gas by itself or oxygen gas diluted with an inert gas. An inert gas denotes a rare gas such as for example argon or helium, or nitrogen gas, or mixtures thereof. Reactive vapour deposition is a technique in which evaporation is effected from a metal or metal oxide in an oxidizing atmosphere, and an oxidation reaction brought about in the vicinity of the substrate layer so that formation is effected on the substrate layer. The evaporation source for such purposes may have a boat form of resistance heating system or a crucible form based on radiant or high frequency heating, or there may be used a system based on electron beam heating, but there are no particular restrictions thereon.
In the case where the inorganic thin film is a metal oxide, it is most preferred that it be totally the oxide but, generally speaking, when trying to totally form the oxide there is a high likelihood of producing regions which are over-oxidized and where the gas barrier properties are inferior such that it is difficult to obtain high overall gas barrier performance. Hence, the inorganic thin film may be an incompletely-oxidized film in which some metal component remains. Where used as a packaging bag, the light transmittance of the vapour-deposited film is preferably at least 70%, more preferably at least 80% and still more preferably at least 85%, from the point of view of being able to confirm the quality of the contents. The upper limit of light transmittance is restricted by the light transmittance of the polyester film in the present invention, and since the upper limit of the light transmittance of such film is 92%, the essential upper limit of light transmittance is 92%.
With regard to the thickness of the inorganic thin film, in the case of an aluminium thin film there is used a thickness of 20 to 50 nm and, by optical density (the logarithm of the reciprocal of the light transmittance) there is deposited material giving a value of 1.5 to 3 approximately. In the case of a metal oxide, from the point of view of the gas barrier properties and flexibility, there is preferably used a thickness in the range S to 100 nm and more preferably 8 to 50 nm. With less than 5 nm, the barrier properties are inadequate, while if the film thickness exceeds 100 nm, as a result of the latent heat of condensation of the metal oxide at the time of vapour-deposition there occurs thermal damage where the outermost surface of the film melts and whitens, and the flexibility of the vapour-deposited film deteriorates. Furthermore, if the film is folded-over or the like, splitting or peeling of the vapour-deposited film readily occurs. Hence, this is undesirable.
It is possible to provide a layer of other resin on the inorganic thin-film vapour-deposited face of the vapour-deposited film. As said other resin, a film comprising for example a polyolefin resin, nylon resin or polyethylene terephthalate film is preferred, and said film may be biaxially-drawn or undrawn. In the case of lamination to provide a heat-seal layer, an undrawn film of polyolefin resin is preferred, and it is desirable that such film be laminated by the extrusion-lamination method or by means of an adhesive agent. Such vapour-deposited film is used as a packaging bag by superimposing heat-seal layers, and then sealing.
The film of the present invention can be produced using any conventionally-known method. For example, in the case of biaxially-drawn film, the polymers which constitute polyester A, polymer B and polyamide C are dried using an ordinary hopper dryer, paddle dryer, vacuum dryer or the like, after which they are respectively supplied to separate extruders and melt extruded at 200-320xc2x0 C. via a slit-shaped three-layer die, and rapidly cooled, to produce an undrawn laminate film of polyester A/polymer B/polyamide C. In the case where the T-die method is used, by employing the so-called electrostatic pinning method at the time of the rapid cooling it is possible to obtain a film of uniform thickness, and this is preferred. Next, methods for simultaneously or sequentially biaxially-drawing the undrawn film are described. In the case of sequential biaxial drawing, the order of drawing may be in the film lengthwise direction and then the widthwise direction, or the reverse. Furthermore, in sequential biaxial drawing, the lengthwise direction or widthwise direction drawing can be carried out twice or more. The method of drawing is not particularly restricted, and there may be used methods such as roll drawing or stenter drawing, and the formed film shape may be flat, tubular or the like. The lengthwise direction and widthwise direction draw ratios can be freely set according to the desired orientation and suitability for vapour-deposition but they are preferably in the range 1.5 to 6.0. The drawing temperature may be any temperature lying in the range between the glass transition temperature of the polyester and the crystallization temperature but, normally, from 30 to 150xc2x0 C. is preferred. Furthermore, following the biaxial drawing, heat treatment of the film can be carried out. The heat treatment temperature can be any temperature below the melting point of polyester A but, preferably, it is in the range from 200 to 240xc2x0 C. The heat -treatment may be carried out while allowing the film to relax in the lengthwise direction and/or the widthwise direction.
Next, before the vapour-deposition, the surface (polyamide C layer) of the film of the present invention which is to undergo vapour deposition may be given a known treatment to promote adhesion, for example it may be subjected to a corona discharge treatment in air or in some other kind of atmosphere, or to a flame treatment or a UV treatment. In the case of a corona discharge treatment, the gas atmosphere may be air, carbon dioxide or a mixed system of nitrogen/carbon dioxide and, in particular, when the corona treatment is carried out in carbon dioxide or a nitrogen/carbon dioxide mixed gas (volume ratio in the range 95/5 to 50/50), the surface wetting tension of the film surface will be at least 35 mN/m, so this is preferred.
Next, the film of the present invention is set in a vacuum deposition device equipped with a film travel device, and said film is made to travel via a cooling metal drum. While so-doing, aluminium metal is heated and caused to evaporate, and vapour-deposition is carried out. Alternatively, oxygen gas is supplied to the location of evaporation/vaporization and, while oxidizing the aluminium, condensation and deposition take place on the travelling film, forming an aluminium oxide vapour-deposited layer, and the film is then wound up. By varying the ratio of the amount of aluminium. evaporated at this time and the amount of oxygen gas supplied, it is possible to vary the light transmittance of the aluminium oxide vapour-deposited film. Following the vapour-deposition, the interior of the vacuum deposition device is returned to normal pressure and the wound film is slit. When ageing is carried out by leaving for at least one day at a temperature of at least 30xc2x0 C., the gas barrier is properties are stabilized, so this is preferred.